Seals for shafts with rotating, helical or reciprocating motion function either axially, so called axial face seals, or radially. A good sealing effect is obtained if the mass of those sealing parts following the radial and axial movements is as small as possible. Here radial seals have decisive advantages as opposed to axial face seals, as the agitated mass of said radial seals only amounts to a fraction of that of an axial face seal.
It is known to seal even large shafts with diameters greater than one meter with radial and axial face seals of various types. One type of radial seal frequently used, is the shaft seal ring consisting of a rubber lip which abuts in a sealing manner against the shaft periphery under a radially inwards directed force which is generated by a helical spring closed to form a ring. The rubber part is idle, and inserted into the idle machine part with its outer periphery acting in a sealing manner. With the self-elasticity of the rubber material and with the lever existing between the sealing lip and the adjustment in the idle machine part, the shaft sealing ring can absorb certain inclined positions and radial vibrations as well as frequently occurring excentricity of the shaft against the idle machine part.
The design of such a shaft sealing ring preferrably used hitherto, is however limited in view of the shaft diameter and in view of the operating pressure in the medium to be sealed. Attempts have been made to obtain a better sealing effect with higher pressures by means of a thrust ring on the low pressure side, behind the sealing lip and thus preventing a protrusion of the elastic lip in the gap between the shaft and the idle machine part. By flanging or pressing the sealing ring in the casing, said sealing ring can follow the radial displacements of the shaft, resulting from wear of the supporting bearing, from excentricity caused by false, incorrect installation or from shock-like occuring radial forces. With such a positioning error of the shaft, the seal is very strongly pressed together by the shaft on one side and the sealing lip loses contact with the shaft at the diametrically opposite point, despite the certain equalization caused by the elasticity of the material of the sealing lip. A result thereof is a severe leakage where the lip no longer has sealing contact with the shaft on the one hand, and an intensive wear of the shaft caused by an enforced contact pressure at the diametrically opposite point on the other hand.